The present invention relates to a drive control apparatus for a brushless motor that controls the timing with which current is supplied to exciting coils based upon signals provided by Hall elements that detect the position of a rotor.
A brushless motor in the prior art comprises a rotor provided with permanent magnets, a stator provided with exciting coils wound around it for imparting a rotating magnetic field to the rotor, Hall elements that detect the position of the rotor and switching elements constituted of FETs or the like that switch the exciting coils to which electric current is supplied as disclosed in, for instance, Japanese Unexamined Patent Publication No. S 60-204286 and Japanese Unexamined Patent Publication No. H 5-91789. The timing of switching performed by the switching elements, i.e. the timing with which power is supplied to the exciting coils, is controlled based upon output signals from the Hall elements
However, in the structure described above, if the timing with which power is supplied to the exciting coils is set in advance with the output efficiency of the motor as a primary factor, while no significant problems arise in the high speed rotation range, there is a problem in that, the noise of the motor in the low speed rotation range increases. If, on the other hand, the power supply timing is set with priority given to reducing the motor noise, while no significant problem arises in the low speed rotation range, there is a problem in that the output of the motor becomes insufficient in the high speed rotation range, when a large output is required.
Generally speaking, it is desirable to give priority to noise reduction in the low speed rotation range even though it somewhat reduces the output efficiency of the motor, since the need for driving the motor is not so stringent in this range, whereas it is desirable to give priority to achieving a high degree of output efficiency for the motor over a reduction in the noise in the high speed rotation range, since the need for driving the motor is acute in this range.